In the production of foamed, cellular or expanded synthetic resins, e.g. foamed polyurethane, it is known to incorporate a gas in the synthetic-resin mixture and to permit expansion of the gas with setting of the product so that the latter will have a cellular, reticulate or foamed conformation.
One way of incorporating a gas in the reaction mixture, of course, is to charge one of the liquid components of the reaction system with the gas under pressure or by some other means.
The degree to which this component has been charged with the gas is a reflection on the nature of the quality of the product and thus it is desirable from time to time to measure the gas charge introduced into or the gas loading of a liquid synthetic resin component.
In U.S. Pat. No. 4,089,206, there is described a method of and an apparatus for measuring the proportion of undissolved gas in a liquid component for the production of foam materials in which the sample of liquid component is periodically diverted from the tank containing same into a measuring vessel.
In this system, the measuring vessel is in effect a decompression chamber and the measurement is carried out by determining the rise in a liquid column as a result of its decompression.
Measurement in this fashion is particularly slow and awkward since the decompression of the liquid column is a comparatively slow process. Furthermore, the accuracy of the process is poor when the liquid component is also provided with a solid charge of reinforcing or extending solid particles such as glass fibers. One of the problems with the measurement precision is that the variable level to which the decompression chamber is filled cannot be readily detected by the eye and can only be controlled with the requisite precision and speed with complex and extensive means. Furthermore, with this system, it is only possible to obtain relative values of the density and not an absolute value which is frequently necessary.